Due to advances in modern medicine, the elderly population is growing worldwide, and, along with this growth, there is a growing need for physical rehabilitation after strokes, which have an average onset of over 65 years of age. Given the magnitude of this problem and its societal ramifications, the time is ripe to explore the extent to which robotic devices and virtual environments can be used as a means of rehabilitation to improve the quality of life for both the elderly and the physically disabled. According to recent studies in robotics, robot-assisted stroke rehabilitation enhances arm movement recovery. Moreover, robot-assisted rehabilitation improves patients' mobility and strength to the point where it is equal to, or greater than, that which is achieved by human-assisted therapy. However, none of the currently available systems addresses patients' perceptual or cognitive deficits. Furthermore, these systems neglect to address the fact that many patients do not reach their full mobility potential using these systems. To remedy these problems, a virtual robotic environment that explores the full potential needs and abilities of patients must be developed. We will coin this strategy, "rehabilitation by distortion." To develop an environment to rehabilitate by distortion, however, there are two fundamental issues to address. First, it is necessary to quantify the perceptual gap that can be created between virtual and actual movements that is not perceptible to patients. To do so, we will first quantify the lowest sensory resolution, also known as just noticeable difference (JND), of force and position. As we explain below, the JND will act as the lowest bound of the perceptual gap. In addition, we will quantify the size of the perceptual gap with the existence of visual feedback distortion. Second, having identified a perceptual gap that is not noticeable, we must prove that mobility and strength of stroke patients can be extended by undetected distortion. For this proposed work, we will isolate working with one finger. Fingers are one of the parts of the body that are most commonly affected by strokes; thus testing the basic concepts about the perceptual gap between virtual and actual movements using fingers is appropriate. After we prove that rehabilitation by distortion is therapeutic for a finger, we can expand our work to other limbs. In addition, to show that this strategy is effective for patients who already received traditional therapy, we will work with patients who have already completed their traditional therapy and are at least one year after the onset of strokes. If we prove that we can allow patients to move beyond what they thought was possible after traditional therapeutic techniques, the results will be groundbreaking and will lead to an R01 grant to develop a new robotic virtual therapeutic strategy, "rehabilitation by distortion," that extends the force production and range of motion for motor impaired patients recovering from stroke. [unreadable] [unreadable]